1 Measuring Refractive Indices of Nematic LC Elastomers Volodymyr Borshch Research advisor: Professor Peter Palffy-Muhoray 25 August 2008

2 Outline Motivation Nematic LC elastomer Methods and previous results Theory Materials selection Experimental setup Obtained data Conclusions Acknowledgments

3 Motivation Nematic LC Elastomers have bright future Not all physical properties are quite extensively described so far E.g. Refractive index

4 Nematic LC elastomer O O O O Mesogen O CH 3 H Si O CH 3 Si H CH 3 Si H 85 CH 3 Backbone CH 2 O O Crosslinker From Israel Lazo presentation

5 Methods Israel Lazo presentation

6 Yet another approach From Fresnel equations: The main idea of the method R=0

7 High refractive index liquids Liquids at or near 20˚C Refractive indexMaterial 1.627Quinoline 1.660α-Monobromonaphthalene 1.717Mercury potassium iodide 1.737Methylene iodide 1.78Methylene iodide and sulphur (saturated) 1.793Barium mercuric iodide aq. 1.82Potassium iodide and mercuric iodide aq Solutions of 35% by weight CH 2 I 2, 31% SnI 4, 16% AsI 3, 8% SbI 3 and 10% S 1.885Hydrogen disulphide 1.95Phosphorus in carbon disulphide 2.06Yellow phosphorus 8 parts by weight + 1part sulphur + 1 methylene iodide 2.2Mercuric iodide in aniline or quinoline Data from Kaye and Laby, Tables of Physical and Chemical Constants, 1959 Ionic liquids based on 1- alkyl-3- methylimidazolium cations Most of them were either: - Highly toxic and poisonous - Not transparent - Not available A simple, cost-effective and magnificent liquid was used – saturated solution of NaI n = 1.496

8 Experiment HeNe Rotating polarizer Fish tank with immersed elastomer Experimental setup Measuring the reflectance of the elastomer in normal incidence λ/4 plate detector nm filter Reference beam Beam splitter lens Lock-in amplifier detector

9 n o measurement The polarization is perpendicular to the preferred director orientation n elastomer with no strain batch #71 (10% cross linkers) Fitting and extrapolation gives n= ± The sample from batch #69 gave similar value n=

10 n e measurement The polarization is parallel to the preferred director orientation n elastomer with no strain batch #71 (10% cross linkers) Fitting and extrapolation gives n = ±

11 Benefits and drawbacks of the method Looks simple Inhomogeneity of elastomer Scattering

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13 Conclusions The sample was different but the results agree with previous measurements The refractive indices need to be measured more accurately Future work: Generalized Ellipsometry Need to measure inhomogeneity

14 Acknowledgement Prof.Peter Palffy-Muhoray Jake Fontana, Israel Lazo Paul Luchette, Michele Fontana Jeremy Neal, Sabrina Relaix Rafael Zola

15 Thank you !